Walk behind lawn mowers are well known outdoor power equipment units for mowing grass. Such mowers comprise a movable cutting deck having a cutting chamber that carries a substantially horizontal rotary cutting blade. A handle extends upwardly and rearwardly from the cutting deck. An operator grips a handle grip on the handle and walks behind the mower to guide and control the mower.
The cutting chamber is formed on the underside of the cutting deck and includes a top wall and a downwardly extending, peripheral side wall. The cutting chamber has an open bottom facing the ground so that the blade rotating inside the cutting chamber can contact and sever grass as the cutting chamber moves over the ground. The cutting chamber often includes a central hub that defines an annular channel between the hub and the sidewall of the cutting chamber. The grass clippings created by the blade will circulate through at least a portion of this annular channel before exiting the cutting chamber through an exit tunnel.
The exit tunnel is typically U-shaped having a top wall and spaced apart side walls. The exit tunnel rises in height from a front end thereof to a rear end thereof. The exit tunnel receives the grass clippings from the cutting chamber and conducts the grass clippings to a rear discharge opening on the exit tunnel. The grass clippings can be discharged through the discharge opening onto the ground or can be collected in a grass collection container when such a container is connected to the discharge opening. This is the discharge/collection mode of operation of the lawn mower.
The rear discharge opening of the exit tunnel can be selectively closed by a pivotal door which pivots about a substantially horizontal pivot axis adjacent the top wall at the rear of the exit tunnel. Thus, the door can be pivoted upwardly and forwardly inside the exit tunnel to lie flat against the top wall of the exit tunnel to open the rear discharge opening when the mower is in the aforementioned discharge/collection mode of operation. Alternatively, the door can be pivoted rearwardly and downwardly to hang generally vertically downwardly from its pivot axis to block or close the rear discharge opening of the exit tunnel. This places the mower in a mulching mode of operation.
When a mower is placed into its mulching mode simply by closing the pivotal door at the rear of the exit tunnel, this leaves the length of the exit tunnel forward of the door open to the cutting chamber. Thus, grass clippings can still enter the exit tunnel and will quickly pack inside the exit tunnel against the closed door. This will detract from the mulching performance of the mower since grass clippings can dribble or fall out of the front of the tunnel in an unpredictable manner and leave clumps of clippings on the ground. In addition, the packed clippings have to be cleaned out of the exit tunnel from the inside of the cutting chamber in order to open the pivotal door to place the mower into its discharge/collection mode of operation.
Some mowers of this type use a grass plug that can be inserted into the exit tunnel through the rear discharge opening when the pivotal door is open. The grass plug extends the length of the tunnel and keeps grass from entering the tunnel when the plug is in place. The insertion of the plug places the mower into its mulching mode of operation without having to close the pivotal door. U.S. Pat. No. 4,951,449 to Thorud, which is assigned to The Toro Company, the assignee of this invention, shows a mower of this type, i.e. a mower with a grass plug insertable into the exit tunnel to place the mower into its mulching mode of operation.
The grass plug approach to blocking the exit tunnel has a number of disadvantages. First, the grass plug can be quite difficult to remove from the exit tunnel after it has been in place for a period of time because dirt and grass clippings wedge between the walls of the plug and the walls of the exit tunnel. Thus, some users may not use the grass plug and instead may use only the pivotal door to block off the exit tunnel in the mulching mode of operation, thereby leading to the tunnel plugging difficulties which use of the grass plug was intended to overcome. Secondly, the grass plug is a separate part and is prone to being lost or misplaced. If the grass plug is misplaced or not readily at hand, the mower can be placed into the mulching mode of operation only by closing the pivotal door at the rear of the exit tunnel.
Moreover, using an exit tunnel to lead grass clippings out of a cutting chamber inherently detracts from the mulching performance of a lawn mower because the clippings are intended to travel in a path that leads out of the cutting chamber rather than encouraging the clippings to remain in the cutting chamber and being driven down into the cut grass path. Some mulching mowers are dedicated mowers in which the cutting chamber has no exits and whose shape is optimized to permit recirculation of the grass clippings and their eventual deposition in the cut grass path. However, such dedicated mulching mowers are not as desirable to many consumers as mowers which can be converted between a discharge/collection mode and a mulching mode of operation since such mowers cannot be used to bag the clippings. Accordingly, there is a need in the mower art for a mower which can be easily converted between the discharge/collection and mulching modes of operation and whose performance in the mulching mode of operation approaches that of a dedicated mulching mower.